Three-dimensional polymer composite parts can be manufactured using different methods, one of which is liquid molding. Resin Transfer Molding (RTM) and VARTM are examples of manufacturing processes that involve injecting a liquid resin into a fibrous preform. During the RTM process, the preform is placed into an enclosed mold cavity, and the resin is injected into the cavity under pressure. The mold with the preform is often put under vacuum so that the vacuum removes all the entrapped air in the preform and speeds up the RTM process. Once the liquid resin fills the mold cavity, the resin is cured, resulting in the formation of a composite part. VARTM is similar to RTM except that a single-sided tool is normally used with vacuum bagging, and vacuum pulls the liquid resin into the preform. These techniques are well suited for the manufacturing of very complex-shape parts, in many cases at reasonable production rates. The fiber architecture, permeability of the preform and the fabric crimps, resin viscosity, and temperature of operation have an influence on the wetting of the fabric.
To prepare the preform, dry layers of unidirectional reinforcing fibers or woven fabrics are laid up similarly to the way resin-impregnated prepregs are laid up. It would be desirable to employ Automated Tape Laying (ATL) and Automated Fiber Placement (AFP) for the lay-up of the preform to reduce costs. However, the technological challenges connected to the manufacture of dry, narrow-width, fibrous products suitable for automated placement processes, such as ATL and AFP, requires further development.